With development of semiconductor integrated circuit (IC) technology, semiconductor devices and interconnect structures are downsized. Such downsizing may result in reduced spacing between metal wirings and also result in reduced thickness of inter-layer dielectric (ILD) layers for isolating adjacent metal wirings. Consequently, crosstalk may occur between the metal wirings. Conventional methods for effectively reducing such crosstalk may include reducing dielectric constant (k) of the ILD layers, i.e., using low-k ILD layers, configured between metal wirings. The low-k ILD layers may also effectively reduce resistance capacitance delay (RC delay) between the metal wirings. For these reasons, low-k and ultra-low-k dielectric materials have been widely used for ILD layers in the interconnect technology. Since air provides minimum k value (k=1.0) among other materials that can be obtained, forming air pores, gaps, or holes in the ILD layers can effectively reduce the k value of the dielectric material. That is, ILD layers formed by porous materials have reduced k value.
In addition, copper interconnect structure is widely used in IC devices. This is because signal transmission between semiconductor devices requires high density of interconnect wirings, and interconnect wirings formed by copper production process can reduce RC delay and improve reliability issues caused by electron migration.
Conventional methods for forming a copper interconnect structure include forming grooves or through holes in a porous ILD layer to form interconnect metal wirings or metal plugs, which requires forming photoresist pattern on the ILD layer. After the grooves or through holes are formed, the photoresist pattern is removed by an ashing method. After removing the photoresist pattern, polymer residues are left in the grooves or through holes, which affects properties of the formed semiconductor device. Before filling copper in these grooves or through holes, a cleaning solution (e.g., EKC solution from DuPont or ST250 solution from ATMI) is needed to wet clean the semiconductor device to remove the polymer residues.
Cleaning solutions are often repeatedly used to reduce cleaning and manufacturing cost. In order to ensure the cleaning effect, after each use, the cleaning solution may be filtered to remove the polymer residues. However, semiconductor devices cleaned in such cleaning solutions may be prone to having time dependent dielectric breakdown (TDDB), which adversely affects device reliability.
Thus, there is a need to provide improved methods and systems for making and/or cleaning semiconductor devices.